Heat recovery system of the boiler with CO2 capture system

ABSTRACT

A boiler system including an electric power generation system having a boiler, a steam turbine for generating electric power by steams which received heat at a boiler, a condenser provided at the downstream thereof for condensing the steams, and a heater for heating condensed water by steams extracted from the steam turbine and, further, a CO 2  capture system of sorbing and capturing a CO 2  gas in an exhausted gas exhausted from the boiler by using a solid CO 2  sorbent, and a chimney of exhausting an exhaust gas in the CO 2  capture system after recovery of CO 2  or an exhaust gas exhausted from the boiler, in which the temperature of a fluid concerned with the boiler system is increased by using the exhaust gas exhausted from the CO 2  capture system.

PRIORITY STATEMENT

The present application hereby claims priority under 35 U.S.C. §119 onJapanese patent application number JP 2011-197834 filed Sep. 12, 2011,the entire contents of which is hereby incorporated herein by reference.

BACKGROUND

The present invention concerns a heat recovery system of a boiler with aCO₂ capture system.

In recent years, reduction of CO₂ emission has been demanded world widefor suppressing global warming. Particularly, exhaust gases dischargedfrom equipment such as coal-fired boilers, gas turbines, and chemicalplants contain CO₂ as much as several % or more and a method ofseparating and capturing CO₂ has been demanded.

An exhaust gas processing system of a coal-fired boiler includes anNO_(x) reduction system provided downstream of a boiler for reductionand detoxification of nitrogen oxides (hereinafter referred to asNO_(x)), an air heater provided downstream thereof for cooling anexhaust gas using air as a coolant, a heat exchanger provided downstreamthereof for cooling the exhaust gas using water as a coolant, a dustremoval system provided downstream thereof for removing dusts and sootsin the exhaust gas, a desulfurization system provided downstream thereoffor absorption and detoxification of sulfur oxide (hereinafter referredto as SO_(x)), and a heat exchanger provided downstream thereof forwarming the exhaust gas (for example, refer to IHI Technical Report Vol.45, No. 1 (2005-3) (hereinafter referred to as Non-Patent Document 1).Water heated by the heat exchanger downstream of the air heater isutilized as a heat source for the heat exchanger provided downstream ofthe desulfurization system. Hereinafter, the former heat exchanger isreferred to as a heat recovery heat exchanger and the latter heatexchanger is referred to as a re-heating heat exchanger. The re-heatingheat exchanger is provided for preventing steams discharged out of achimney from forming white smoke that results in visual pollution. In aplace where such regulation is imposed, installation of the re-heatingheat exchanger is legally obliged.

Further, CO₂ in the exhaust gas can be separated and captured byproviding a CO₂ capture system downstream of a desulfurization system.As a method of separating and capturing CO₂ in the exhaust gas, a methodof absorbing CO₂ in a CO₂ adsorbing column by using an amine solutionincluding MEA (monoethanol amine), etc. which is applied to separationand capture of CO₂ in the exhaust gas from a boiler or a gas turbine.For improving a CO₂ capturing efficiency, various amine compounds havebeen proposed (for example, refer to Japanese Patent Publications Nos.3761960 and 3771708). The amine compound has a high ability ofseparating and capturing CO₂. However, since the amine compound ispoisoned by oxygen or SO_(x), etc. in the exhaust gas or scatterspartially from the CO₂ absorption column, supplementation of the aminecompound is necessary to increase the cost.

Then, a CO₂ capture system using a CO₂ solid sorbent which is lesspoisoned by oxygen, SO_(x), etc. in the exhaust gas and less scattershas been studied. For example, a system of having four columns packedwith a CO₂ solid sorbent and capturing CO₂ by four steps of (1) sorbingCO₂ by a sorbent, (2) purging the inside of the column, (3) desorbingCO₂ from the sorbent, and (4) cooling the sorbent is disclosed in NEDOReport, Hei 14 (2002), Development for Effective Utilization ofTechnique of Fixing Carbon Dioxide for Practical Use, and Developmentfor CO₂ Separating and Capturing Technique by Chemical Adsorption, byShikoku Research Institute (2003-3) (hereinafter referred to asNon-Patent Document 2).

Further, a technique capable of downsizing the system by constructing arotational driving type CO₂ capture system using a CO₂ solid sorbent isdescribed in “CO₂ Separation/capture and Store/Isolation Technique”,published from NTS (2009) 76 (hereinafter referred to as Non-PatentDocument 3).

On the other hand, for the heat efficiency of a boiler, a heatefficiency of an electric power generation system is improved generallyby re-heating a condensate generated from a condenser provideddownstream of a steam turbine by steams extracted from the steamturbine.

In a case where the re-heating exchanger is not present, heat recoveredby the heat recovery heat exchanger can be utilized in other uses. Forexample, Japanese Unexamined Patent Application Publication No. S60(1985)-227845 describes a method of heating a condensate by using heatrecovered from a boiler exhaust gas by a heat recovery heat exchangerthereby improving the heat efficiency of the boiler (refer to FIG. 5).

Further, Japanese Patent Unexamined Application Publications Nos. H03(1991)-193116 and 2010-240617 describe that the heat efficiency of aboiler is improved by heating a condensate utilizing the heat ofcaptured CO₂ which is generated from a CO₂ capture system using an aminesolution.

SUMMARY

When CO₂ is recovered by using a CO₂ solid sorbent, heat is generatedupon sorption (absorption heat and adsorption heat) and, further, air,etc. possessing some heat are generated upon cooling of the sorbent. Inthe CO₂ capture system shown in the Non-Patent Documents 2, 3, such heatenergy cannot be re-utilized sufficiently, which may lower the heatefficiency of the boiler due to the energy used for capturing CO₂.Japanese Patent Publications Nos. 3761960 and 3771708 do not describe amethod for coping with the lowering of the heat efficiency of theboiler. The method shown in Japanese Unexamined Patent ApplicationPublication No. S60 (1985)-227845 does not describe the effectiveutilization of heat generated from the CO₂ capture system andimprovement in the heat efficiency is insufficient. Further, since there-heating heat exchanger is not used, this results in a disadvantage ofgenerating white smoke from a chimney. Japanese Unexamined PatentApplication Publication Nos. H03 (1991)-193116 and 2010-240617 only showthe technique of utilizing heat of the CO₂ gas emitted from the aminesolution and do not show an optimal heat recovery method in a case ofusing the CO₂ solid sorbent and improvement in the heat efficiency ofthe boiler is insufficient.

The present invention intends to improve the heat efficiency of a boilerthat separates and captures CO₂ from an exhaust gas using a CO₂ solidsorbent and, specifically, it intends to provide a heat recovery systemand a heat recovery method capable of efficiently recovering the heatenergy generated from a system for capturing CO₂, and a CO₂ sorbent usedtherefor.

A heat recovery system of a boiler according to the invention has a CO₂capture system of capturing CO₂ contained in an exhaust gas by using aCO₂ solid sorbent and increases the temperature of a fluid concernedwith the boiler by using a gas generated from the CO₂ capture system.

According to the invention, the heat efficiency of the boiler can beimproved remarkably by efficiently recovering the heat generated fromthe CO₂ capture system. Further, it can prevent generation of whitesmokes from a chimney while suppressing lowering of the heat efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an embodiment of an existent boiler exhaust gaspurifying system;

FIG. 2 is a view showing a system for improving the heat efficiency of aboiler by an existent method;

FIG. 3 is a view showing a CO₂ capture system using a CO₂ sorbent;

FIG. 4 is a view showing a system for increasing the temperature of acondensate by using an exhaust gas from a CO₂ capture system;

FIG. 5 is a view showing a system for increasing the temperature of agas flowing into a boiler by using an exhaust gas from the CO₂ capturesystem; and

FIG. 6 is a view showing a system for increasing the temperature of agas flowing into a chimney by using an exhaust gas from the CO₂ capturesystem.

DETAILED DESCRIPTION

The present invention is to be described specifically.

Generally, for improving the heat efficiency of a boiler, a steamturbine that generates electric power by steams which received heat at aboiler and a condenser for condensing the steams at the downstreamthereof are provided, and a condensate obtained by condensation isheated by steams extracted from the steam turbine, thereby improving theheat efficiency of the electric power generation system. Further, inJapanese Unexamined Patent Application Publication No. S60(1985)-227845, the heat efficiency of the power generation system isfurther improved by heating water condensed by the condenser using theheat of a boiler exhaust gas by passing through a heat exchanger.However, since the heat of the boiler exhaust gas is used for increasingthe temperature of the condensate, the temperature of the exhaust gas atthe upstream of a chimney cannot be increased, which may possibly leadto generation of the white smoke.

The present inventors have made an earnest study and, as a result, havefound that white smoke generated from a chimney can be suppressed whilealso improving the heat efficiency of an electric power generationsystem in a boiler system comprising a power generation system having aboiler, a steam turbine that generates electric power by steams whichreceived heat at a boiler, a condenser provided at the downstreamthereof for condensing the steams, a heater for heating the condensedwater with steams extracted from the steam turbine and, further, a CO₂capture system for sorbing and capturing a CO₂ gas in an exhaust gasexhausted from the boiler by a solid CO₂ sorbent, and a chimney fordischarging the exhaust gas after capturing CO₂ by the CO₂ capturesystem, or an exhaust gas exhausted from the boiler, in which thetemperature of a fluid concerned with the boiler system is increased byusing the exhaust gas exhausted from the CO₂ capture system.

The boiler as a target of the invention is not particularly restrictedso long as a heat recovering steam turbine is provided. The invention isapplicable to a system including a gas-fired boiler, a coal-firedboiler, or a gas turbine as the boiler, as well as to IGCC (integratedcoal gasification combined cycle).

As the fluid concerned with the boiler system, water condensed by thecondenser, a gas flowing into the boiler, and an exhaust gas exhaustedfrom the boiler may be considered.

(Increase of Temperature of Condensate)

The heat efficiency of the electric power generation system can beimproved by partially or entirely heat-exchanging water condensed by thecondenser with the exhaust gas exhausted from the CO₂ capture system byusing a heat exchanger and increasing the temperature thereof. In theinvention, a solid CO₂ sorbent is used as the CO₂ capture system. Inthis case, the temperature of the exhaust gas exhausted from the CO₂capture system may sometimes reach 100° C. to 500° C. depending on thetype of the CO₂ sorbent. Japanese Unexamined Patent ApplicationPublication No. H03 (1991)-193116 describes that the turbine output isimproved by 0.3% to 0.4% based on a trial calculation in a case of a CO₂exhaust temperature at 85° C. When a solid CO₂ sorbent is used, afurther improvement can be expected in the turbine output.

Further, in this case, white smoke can be prevented, for example, byrecovering the heat of the boiler exhaust gas at the downstream of theair heater by the heat recovery heat exchanger and increasing thetemperature of the exhaust gas at the upstream of the chimney by usingthe re-heating heat exchanger.

(Increase of Temperature of Gas Flowing into Boiler)

The heat efficiency of the boiler is improved by increasing thetemperature of a gas flowing into the boiler by using the exhaust gasexhausted from the CO₂ capture system. In the existent technique, air atabout room temperature is heated to about 300° C. by using an air heaterand then caused to flow into the boiler. However, when the temperatureof air is increased to about 100° C. by using the exhaust gas exhaustedfrom the CO₂ capture system, the temperature of the air flowing into theboiler after passing through the air heater can also be increased toabout 350° C. In this case, since the temperature of the boiler exhaustgas is increased by about 50° C., when a heat recovery heat exchanger isprovided to the downstream of the air heater and the temperature ofwater condensed by the condenser can be increased partially or entirelymore effectively by using the heat exchanger, and the heat efficiency ofthe electric power generation system is improved. In this case, theelectric power generation efficiency of the boiler is improved by about2.1%.

Further, in this case, white smoke can be prevented effectively bypartially or entirely using the heat recovered by the heat recovery heatexchanger for increasing the temperature of the exhaust gas at theupstream of the chimney by using a re-heating heat exchanger.

Means for increasing the temperature of the gas flowing into the boilerby using the exhaust gas exhausted from the CO₂ capture system is notparticularly restricted. For example, the exhaust gas exhausted from theCO₂ capture system and a gas including air can be heat-exchanged byusing a heat exchanger. Species of a gas generated from the CO₂ capturesystem include, for example, N₂, O₂, CO₂, H₂O, air, etc. In this case,there is a merit that the gas can be used irrespective of the species.

Alternatively, the exhaust gas exhausted from the CO₂ capture system canbe used partially or entirely as a gas flowing into the boiler. Theexhaust gas generated from the CO₂ capture system may sometimes containCO₂, which may lower the CO₂ recovery efficiency if the gas is releasedto atmospheric air. By letting the exhaust gas generated from the CO₂capture system partially or entirely flow into the boiler, CO₂ is againtaken into the boiler and flows through the exhaust gas purificationsystem into the CO₂ capture system to improve the CO₂ capturingefficiency.

(Increase of Temperature of Boiler Exhaust Gas)

Generation of white smoke from the chimney can be suppressed byincreasing the temperature of a gas flowing into the chimney by usingthe exhaust gas exhausted from the CO₂ capture system. Specifically, thetemperature of the gas flowing into the chimney can be increased whenthe gas flowing into the chimney partially or entirely comprises theexhaust gas exhausted from the CO₂ capture system.

Alternatively, the temperature of the gas flowing into the chimney canbe increased by providing a heat exchanger for increasing thetemperature of a gas flowing into the chimney and performing heatexchange with the exhaust gas exhausted from the CO₂ capture system.When the exhaust gas generated from the CO₂ capture system contains CO₂and flows as it is into the chimney, once captured CO₂ is emitted intoatmospheric air. In a case of using the heat exchanger, since the CO₂gas after heat exchange can be captured by flowing CO₂ after heatexchange into a compressor, such disadvantage can be overcome.

(CO₂ Capture System)

The CO₂ capture system is not particularly restricted providing that thesystem utilizes the CO₂ sorbing effect of the solid CO₂ sorbent. As theCO₂ capture system, it may be considered to provide four CO₂ sorbingcolumns packed with a CO₂ sorbent. In this case, as the CO₂ capturingprocess, (a) CO₂ sorbing step, (b) purging step for the inside of theCO₂ sorption column, (c) desorbing step of CO₂ and (d) cooling step forthe inside of the CO₂ sorption column may be considered and CO₂ in theexhaust gas can be captured at a high level by corresponding thefollowing four steps (a) to (d) successively to each of the four CO₂sorption columns.

(a) CO₂ sorption: CO₂ gas in the exhaust gas is sorbed by letting anexhaust gas flow into the CO₂ sorption column.

(b) Purging for the inside of CO₂ sorption column: After sorbing CO₂,inside of the CO₂ sorption column is purged by flowing a gas into theCO₂ sorption column. As a purge gas, a CO₂ gas at a high purity is usedpreferably for increasing the concentration of captured CO₂.(c) CO₂ desorption: Then, a gas is caused to flow for desorbing CO₂ fromthe sorbent and the desorbed CO₂ gas is captured. For desorbing CO₂ fromthe sorbent, it is necessary to heat the sorbent. The quantity of heatto be applied is different depending on the sorbent. It is necessary toincrease the temperature of the sorbent to a temperature at which CO₂ isdesorbed from the sorbent. As a method of applying the heat, it may beconsidered, for example, to extract steams generated in the steamturbine and cause the steams to flow through the CO₂ sorption column.Further, a method of obtaining heat from other CO₂ sorption column byway of a heat exchanger may also be considered.(d) Cooling for the inside of the CO₂ sorption column: Further, it isnecessary to lower the temperature of the sorption column once increasedin the CO₂ desorption step described above to a temperature suitable tothe CO₂ sorbing step. As a method of lowering the temperature, it may beconsidered to flow a gas at a temperature lower than that of thesorption column. Use of atmospheric air at room temperature may beconsidered as an example. Further, (b) when the CO₂ gas is used forpurging in the purging step for the inside of the CO₂ sorption column,CO₂ may sometimes flow out of the CO₂ sorption column. In this case, thegas flowing out of the CO₂ sorption column can also be used as a gas forlowering the temperature of the CO₂ sorption column by letting the gasflow into the CO₂ sorption column during the cooling step (d) in the CO₂sorption column. By using the method, CO₂ once flowing out in thepurging step can be caused to flow again into the sorption column toimprove the CO₂ recovery efficiency. Japanese Unexamined PatentApplication Publication Nos. H03 (1991)-193116 and 2010-240617 disclosea technique of recovering the heat of the CO₂ gas desorbed from theamine solution, but any gas generated from the CO₂ sorption column atthe steps (a) to (d) can be used when the solid CO₂ sorbent is used.

The gas flowing out of the CO₂ sorption column may include, for example,N₂, O₂, CO₂, steams, air, etc. Since the flowing out gas has a sorptionheat in the sorption column (adsorption heat, absorption heat, heattransferred from the sorbent), etc. the gas reaches a temperature atabout 50° C. to 500° C. By recovering the heat of the flowing out gas bythe technique shown in the present specification, the heat efficiency ofthe electric power generation system can be improved.

The CO₂ sorbing material is not particularly restricted so long as thesorbent comprises a material capable of sorbing CO₂ and preferredingredient includes, for example, Ce, Pr, Nd, Sm, Gd, etc. The CO₂recovery efficiency is improved particularly by the use of Ce. Thechemical form of the ingredient is not particularly restricted. Thechemical form of the ingredient may include, for example, metal, oxide,organic compound, and chloride, and the oxide form is particularlypreferred. The oxide suffers from less degradation due to the use andcan be used for a long time.

The structural form of the CO₂ sorbent includes, for example, that ofgranule, lump, sphere, pellet, honeycomb, mesh, etc. and the structuralform can be selected in accordance with the operation state of the CO₂capture system, to which the sorbent is applied.

The CO₂ sorbent preferably has a specific surface area of 3 m²/g ormore. When the specific surface area is small, the CO₂ capturingperformance is decreased and the provision of the system gives lesseffect.

The ingredient may be supported, for example, on a porous support suchas alumina or zeolite. The ingredient can be dispersed highly and theCO₂ sorbing performance can be improved further by supporting theingredient on the porous support having a specific surface area of 10m²/g or more.

As the preparation method of the CO₂ sorbent, physical preparationmethod, for example, an impregnation method, a kneading method, acoprecipitation method, a sol-gel method, an ion exchange method, avapor deposition method, a spray dry method, etc., and preparationmethods utilizing the chemical reaction can be used.

As the starting material for the CO₂ sorbent, various compounds, forexample, nitrate compounds, chlorides, acetate compounds, complexcompounds, hydroxides, carbonate compounds, and organic compounds, aswell as metals, or metal oxides can be used.

Preferred embodiments of the invention are to be described withreference to the drawings.

(Example of Existent Exhaust Gas Purifying System)

FIG. 1 shows an example of an exhaust gas processing system for acoal-fired boiler having a CO₂ capture system using a CO₂ solid sorbent.Coal and air are supplied to a coal-fired boiler 1, and the coal isburnt. The temperature of a combustion exhaust gas reaches 1600 to 1800°C. The temperature of the exhaust gas is lowered by a not-illustratedheat exchanger in the boiler and then introduced into an NO_(x)reduction system 2. In the NO_(x) reduction system, ammonia (hereinafterreferred to as NH₃) is supplied to reduce and detoxify NO_(x) intonitrogen (hereinafter referred to as N₂) by using a NO_(x) reductioncatalyst. Further, the exhaust gas is introduced into an air heater 3and heat-exchanged with air 11 (boiler combustion gas). Air 11 issupplied from atmosphere air by a gas supply blower 10 (hereinafterreferred to as FDF), heated by the air heater 3 and used as a combustionair in the coal-fired boiler 1. The exhaust gas introduced into a heatrecovery heat exchanger (hereinafter referred to as a heat recoveryGGH4) is heat-exchanged with water in the heat recovery GGH4, thenremoved with dusts and soots by a dust removal system 5, and removedwith SO_(x) in a desulfurization device 6. On the other hand, thetemperature of the exhaust gas is increased by the reheating exchanger(hereinafter referred to as a reheating GGH8) by using water warmed bythe heat recovery GGH4, and the exhaust gas is released from a chimney 9at such a temperature that steams do not form white smoke. There-heating heat exchanger is provided for preventing visual pollutioncaused by white smoke. If white smoke comprises steams, there is noenvironmental problem and installation thereof may not be legallyobliged depending on the location.

Comparative Embodiment

As a method of improving the heat efficiency by proceeding heat recoveryin the exhaust gas processing of a coal-fired boiler, a technique asshown in FIG. 2 is considered. This technique concerns an exhaust gasprocessing system not providing a re-heating heat exchanger and this isa system of improving the heat efficiency of the boiler by utilizingheat recovered by a heat recovery GGH4.

A steam turbine 23 is driven by heat-recovered steams of a coal-firedboiler 1, and steams at the exit are cooled and condensed by a condenser24. The formed condensate is sent to a heater 26 and heated by steams 25extracted from the steam turbine 23. The heated condensate is sent tothe boiler 1 to drive the steam turbine 23 again as a circulating cycle.

As shown in FIG. 2, a system of partially or entirely passing acondensate generated from the condenser 24 through the heat recoveryGGH4 to increase the temperature of the condensate thereby improving theefficiency of the heat recovery has been considered as the existenttechnique. However, although this method improves the heat efficiency, adisadvantage not capable of preventing generation of white smoke fromthe chimney occurs since the re-heating exchanger is not present.Further, heat generated from the CO₂ capture system cannot be utilized.

First Embodiment Example of CO₂ Capture System

As a CO₂ capture system that can be used in the technique of theinvention, a system shown in FIG. 3 may be considered.

CO₂ sorbent packed columns 20 as containers for incorporating a CO₂sorbent shown by four units in FIG. 3 each have an identical function.Each of the four units of the CO₂ sorbent packed columns 20incorporating the CO₂ sorbent continuously repeats four steps, that is,a CO₂ sorbing step, a CO₂ purging step, a CO₂ desorbing step, and acolumn cooling step successively.

At the first step (CO₂ sorbing step), a CO₂-containing gas which is anexhaust gas flowing from a channel 18 for CO₂-containing gas is causedto flow only to one of the four units of the CO₂ sorbent packed columns20 incorporating the CO₂ sorbent, and CO₂ is sorbed by the CO₂ sorbent.The gas after removing CO₂ is exhausted from a gas exhaust port 21 or apipeline 22 connected with a CO₂ compressor to the outside of thecolumn. After it is judged that CO₂ sorption by the CO₂ sorbent reachessaturation, flow of the CO₂-containing gas from the channel 18 forCO₂-containing gas to the CO₂ sorbent packed column 20 incorporating theCO₂ sorbent is stopped.

At the second step (CO₂ purging step), CO₂ is caused to flow from achannel 15 for high purity CO₂ gas into the CO₂ sorbent packed column 20to purge gases other than CO₂. The gases discharged in this step areexhausted from the gas exhaust port 21 or the pipeline 12 connected withthe CO₂ compressor to the outside of the column. Finally, flow of theCO₂-containing gas is stopped.

At the third step (CO₂ desorbing step), the temperature of the CO₂sorbent packed column 20 is increased and steams are caused to flow froma steam gas channel 16, by which CO₂ sorbed in the CO₂ sorbent isdesorbed and exhausted from the gas exhaust port 21 or the pipeline 22connected with the CO₂ compressor to the outside of the column.

At the fourth step (column cooling step), air at room temperature iscaused to flow from an air channel 17 to the CO₂ sorbent packed column20, by which the CO₂ sorbent and the CO₂ sorbent packed column 20incorporating the CO₂ sorbent are cooled.

By repeating the four steps described above in each of the four units ofcontainers incorporating the CO₂ sorbent, the operation of the system ofcapturing CO₂ continuously from the CO₂-containing gas can be attained.

It is considered that the gas exhausted at each of the steps is at atemperature of about 40° C. to 500° C., depending on the species and thetemperature of the gas flowing into the CO₂ sorbent packed column 20incorporating the CO₂ sorbent and, further, the type of the CO₂ sorbent.

(Example of System to Increase the Temperature of Condensate)

FIG. 4 is a view showing an example of a system for increasing thetemperature of a condensate through heat exchange between a condensateobtained by condensation in a condenser 24, and a gas exhausted from aCO₂ sorbent packed column 20 which as the container for incorporating aCO₂ sorbent. As a gas flowing into a heat recovery GGH4, a gasdischarged from the CO₂ sorbent packed column 20 for incorporating theCO₂ sorbent at any of the CO₂ capturing step, the CO₂ purging step, CO₂desorbing step, and the column cooling step may be used. However, a CO₂gas exhausted from the CO₂ sorbent packed column 20 for incorporatingthe CO₂ sorbent in the CO₂ desorbing step is passed through the heatrecovery GGH4, compressed by a compressor, and then recovered. Thecondensate whose temperature is increased by the heat recovery GGH4 ispassed through a heater 26 and then sent to the boiler 1 therebycontributing to the improvement of the power of the electric powergeneration system. Improvement of 0.4% or more can be expected for theturbine output depending on the capacity of the boiler.

In addition, when the system shown in FIG. 1 is combined, and the heatrecovery GGH4 and the re-heating GGH8 are used together, generation ofwhite smoke from the chimney can also be suppressed.

With the result described above, as shown in this embodiment, the boileroutput can be improved and the generation of the white smoke from thechimney can be suppressed simultaneously in the system of increasing thetemperature of a fluid concerned with the boiler system by using theexhaust gas exhausted from the CO₂ capture system, by adapting thesystem, for example, as the heat recovery GGH4 that performs heatexchange between the condensate and the gas exhausted from the CO₂sorbent packed column 20.

Second Embodiment

FIG. 5 is a view showing an example of a system using a gas exhaustedfrom a CO₂ sorbent packed column 20 as a container for incorporating aCO₂ sorbent as a combustion gas of a boiler 1. The system also has adevice of performing heat exchange between a condensate condensed by acondenser 24 and a boiler exhaust gas through a heat recovery GGH4.

As the gas flowing into a gas supply blower 10, a gas exhausted from aCO₂ sorbent packed column 20 incorporating a CO₂ sorbent in the processof a CO₂ sorbing step, a CO₂ purging step, or a column cooling step canbe used. When the temperature of a gas flowing into an air heater 3 isheated from 30° C. to 100° C. by using the gas exhausted from the CO₂sorbent packed column 20, the temperature of the exhaust gas flowinginto the heat recovery GGH4 is increased by about 50° C. Accordingly,the temperature of the condensate undergoing heat exchange by the heatrecovery GGH4 can be increased effectively to improve the boiler output.In this case, the electric power generation efficiency of the boilersystem is improved by about 2.1%.

Further, when the gas exhausted from the CO₂ sorbent packed column 20 asa container in the CO₂ purging step is used as the gas flowing into thegas supply blower 10, a small amount of CO₂ may sometimes be containedin addition to N₂ and O₂ as the species of the gas exhausted from theCO₂ sorbent packed column 20. In this case, since the CO₂ gas can becaused to flow again into the boiler in this system, the CO₂ gas can besorbed again by the CO₂ capture system by way of the exhaust gaspurification system. Accordingly, CO₂ capturing efficiency is improved.

In this embodiment, the system is adapted to use the gas exhausted fromthe CO₂ sorbent packed column 20 as the combustion gas for the boiler 1.It is also possible to use atmospheric air as a combustion gas for theboiler 1 after increasing the temperature of the atmospheric air by heatexchange with the gas exhausted from the CO₂ sorbent packed column 20.In this case, a gas exhausted from the CO₂ sorbent packed column 20incorporating a CO₂ sorbent at any of the CO₂ sorbing step, the CO₂purging step, the CO₂ desorbing step, and the column cooling step can beused as the gas flowing into the gas supply blower 10.

With the result described above, as shown in this embodiment, the boileroutput can be improved in the system of increasing the temperature ofthe fluid concerned with the boiler system by using the exhaust gasexhausted from the CO₂ capture system, in which the temperature of thegas flowing into the boiler is increased using the exhaust gas exhaustedfrom the CO₂ capture system, by adapting the system such that theexhaust gas exhausted from the CO₂ sorbent packed column 20 partially orentirely comprises the combustion gas flowing to the boiler 1 or byadapting the system, for example, as a heat recovery GGH that performsheat exchange between air and the gas exhausted from the CO₂ sorbentpacked column 20 to increase the temperature of the air and use the airas the combustion gas of the boiler 1.

Third Embodiment

FIG. 6 is a view showing an embodiment of a system of letting a gasexhausted from a CO₂ sorbent packed column 20 as a container forincorporating a CO₂ sorbent flow into a gas at the upstream of a chimney9. As the gas flowing into the gas upstream of the chimney 9, a gasexhausted from the CO₂ sorbent packed column 20 for incorporating theCO₂ sorbent at the CO₂ sorbing step, the CO₂ purging process, or thecolumn cooling step can be used. Generally, the temperature of a gasexhausted from a desulfurization device 6 is at about 40 to 50° C. and,when the temperature of the gas is increased to about 90° C. by flowingthe gas exhausted from the CO₂ sorbent packed column 20 forincorporating the CO₂ sorbent to the gas at the upstream of the chimney9, generation of the white smoke from the chimney 9 can be prevented.Further, the boiler output can be improved also by using the system asshown in FIG. 2 together and performing heat exchange between thecondensate condensed by the condenser 24 and the boiler exhaust gas inthe heat recovery GGH4.

In this embodiment, the system is adapted such that the gas exhaustedfrom the CO₂ sorbent packed column 20 as a gas flowing into the gas atthe upstream of the chimney 9, the temperature of the gas flowing intothe chimney 9. Alternatively, the temperature of the gas flowing intothe chimney 9 can be increased also by performing heat exchange betweenthe gas exhausted from the desulfurization device 6 and the gasexhausted from the CO₂ sorbent packed column 20. As the gas exhaustedfrom the CO₂ sorbent packed column 20, a gas exhausted from the CO₂sorbent packed column 20 incorporating the CO₂ sorbent at any of the CO₂sorbing step, the CO₂ purging step, the CO₂ desorbing step, or thecolumn cooling step can be used.

With the result described above, as shown in this embodiment, the boileroutput can be improved and generation of the white smoke from thechimney can be prevented in a system of increasing the temperature ofthe fluid concerned with a boiler system using the exhaust gas exhaustedfrom the CO₂ capture system by adapting the system such that the gasflowing into the chimney 9 contains the gas exhausted from the CO₂sorbent packed column 20, or adapting the system, for example, as a heatrecovery GGH of increasing the temperature of a gas flowing into thechimney 9 by heat exchange between the gas exhausted from thedesulfurization device 6 and the gas exhausted from the CO₂ sorbentpacked column 20.

The present invention is not restricted to the embodiments describedabove but includes various modified embodiments. For example, theembodiments described above have been described specifically for easyexplanation of the present invention but are not always restricted tothose having all constituent factors described therein. Further, aportion of the constitution of one embodiment can be replaced with theconstitution of other embodiments, or a constitution of one embodimentcan be added to that of other embodiments. Further, for a portion of aconstitution in each of the embodiments, addition, deletion orreplacement of other constitution are possible.

What is claimed is:
 1. A boiler system comprising: an electric powergeneration system including: a boiler; a steam turbine which generateselectric power by steam heated at the boiler; a condenser downstreamthereof for condensing the steam; and a heater which heats condensedwater by steam extracted from the steam turbine; and further a CO₂capture system which sorbs and captures a CO₂ gas in an exhaust gasexhausted from the boiler by using a solid CO₂ sorbent; and a chimneywhich exhausts exhaust gas after recovery of CO₂ in the CO₂ capturesystem or exhausted from the boiler, wherein the system has a device forincreasing a temperature of fluid for the boiler system by using exhaustgas exhausted from the CO₂ capture system, wherein the device forincreasing the temperature of the fluid is a device in which the fluidcontains the exhaust gas exhausted from the CO₂ capture system, andwherein the fluid for the boiler system is either a gas flowing into theboiler or an exhaust gas flowing into the chimney.
 2. The boiler systemaccording to claim 1, wherein the fluid for the boiler system is a gasflowing into the boiler, and the gas flowing into the boiler is furtherheated by an air heater upstream of the boiler.
 3. The boiler systemaccording to claim 1, wherein the fluid is an exhaust gas flowing intothe chimney, wherein the exhaust gas exhausted from the CO₂ capturesystem is a gas exhausted during CO₂ sorbing, CO₂ purging, process orcolumn cooling.
 4. The boiler system according to claim 3, wherein thedevice for increasing the temperature of the fluid is a device at leastpartially using the exhaust gas exhausted from the CO₂ capture system asthe gas flowing into the boiler.
 5. The boiler system according to claim1, wherein the device for increasing the temperature of the fluid is asystem in which the exhaust gas flowing into the chimney contains theexhaust gas exhausted from the CO₂ capture system.
 6. The boiler systemaccording to claim 1, wherein the CO₂ capture system includes a CO₂sorption column into which at least one of the exhaust gas exhaustedfrom the boiler, the CO₂ gas, steam, and air is introduced.
 7. Theboiler system according to claim 1, wherein the CO₂ capture systemincludes plural CO₂ sorption columns arranged so that a gas flowing outof one of the CO₂ sorption columns is caused to flow into another of theCO₂ sorption columns.
 8. The boiler system according to claim 1, whereina solid CO₂ sorbent used for the CO₂ capture system contains Ce.
 9. Theboiler system according to claim 1, wherein the exhaust gas exhaustedfrom the CO₂ capture system is a gas exhausted at any of a CO₂ capturingstep, a CO₂ purging step, a CO₂ desorbing step, or a column coolingstep.